Oh, it's a word with a chunk missing from it.
Most words with chunks missing from them are either abbreviations or typing errors, but there are some words that have had chunks missing for so long that we leap over the gaps in them without even thinking about it.
These words are, rather unkindly, called defective. In English they're all verbs (that is, things that are done, like swimming or dancing or worrying).
Defective verbs are very common: they're mostly little words that we slip into sentences to skew the meaning a bit, like can, may, shall, and must.
For instance, we can't say I'd like to can to waggle my kneecaps. Instead we have to say I'd like to be able to waggle my kneecaps.
Do you must? is, sadly, impossible: so we say Do you have to? without even thinking about it.
Apart from these small common words, there are a few more verbs that have chunks missing. The word beware, for instance. You can say Beware of the gibbon! or you can say You want to beware of the gibbon, but saying He bewared of the gibbon isn't really English.
What can you say instead of He bewared of the gibbon?
He kept a wary eye open for the gibbon?
I think it's the best I can do, anyway.
Word To Use Today: defective. This word is from the Latin word dēficere, to forsake or fail.